1. Field of the Invention
This invention relates generally to optical encoders, and more particularly to an optical encoder having multiple thumbwheels with integral encoder patterns.
2. Description of the Related Art
Control consoles for lighting control systems utilize thumbwheels to allow an operator to enter information into the system by turning the thumbwheels. Optical encoders are commonly used to convert rotary motion of the thumbwheels into electrical pulses, thereby allowing a microprocessor in the control system to sense how fast and in which direction the thumbwheel is being rotated.
FIG. 1 is an exploded view of a prior-art commercially available optical encoder. The encoder 10 includes an encoder disc 12 having an encoder pattern in the form of a circular track 14 of radially oriented lines 16 also referred to as elements. The disc is attached to the end of a shaft 18 which is supported in a cylindrical tube 20 that acts as a bearing. The tube 20 is attached to a cover 22 which encloses the disc 12 within a housing 24. The shaft 18 rotates within the tube, thereby causing the elements in the encoder pattern on the disc to move past sensor 26 which is mounted in the housing 24.
In this example, the disc is opaque, the pattern is comprised of dark elements on a light background, and the sensor is a transceiver that emits light towards the pattern and senses reflected light. As the disc spins in response to a knob or other device attached to the shaft, the alternating dark and light portions of the pattern cause the transceiver to generate electrical pulses that are modulated by how fast the disc is spinning. In other encoders, the disc is transparent with opaque elements, a light source is mounted on one side of the disc, and a receiver is mounted on the other side of the disc so that the light is alternately blocked or passed through the disc to the receiver.
FIG. 2 is a side view of a panel-mounted thumbwheel assembly that utilizes the commercially available optical encoder 10 of FIG. 1. Referring to FIG. 2, the encoder 10 is mounted to the back side of a control panel 28 with a bracket 30. The encoder is attached to the bracket by inserting the tube 20 into a hole in the bracket and securing it with a nut 32 which is threaded onto threads on the outside of tube 20. A thumbwheel 34 is attached to the shaft and protrudes through a slot in the control panel so that an operator can manipulate the thumbwheel from the top of the panel.
A problem with the assembly shown in FIG. 2 is that it is bulky and occupies a large amount of space under the panel. If more than two thumbwheel and encoder assemblies are required, they must be spaced a distance Y apart as this is the combined width of the thumbwheel and encoder. Thus, multiple thumbwheels on a single control panel consume excessive space. A further problem is that the commercially available encoder 10 is expensive. Yet another problem is that the assembly shown in FIG. 2 has a high parts-count, and therefore, is expensive and time-consuming to manufacture.
Accordingly, a need remains for an improved method and apparatus for utilizing thumbwheels to provide information to a control system.
It is therefore an object of the present invention to increase the density of multiple wheel encoders.
It is a further object of the present invention to reduce the cost of manufacturing thumbwheel encoders.
Another object of the present invention is to simplify the design and improve the reliability of thumbwheel encoders.
To achieve these and other objects, an encoder assembly in accordance with the present invention utilizes thumbwheels having encoder patterns formed integrally with the wheels. This reduces the space required to mount multiple thumbwheels on a control panel. An encoder pattern comprising two tracks of reflective dots is attached to the side of each wheel. Two optical transceivers are mounted on a printed circuit board next to each wheel so that the pattern elements in each of the tracks move past one of the transceivers as the wheels rotate. The transceivers send electrical pulses to a microprocessor each time a dot passes a transceiver. The dots in the two tracks are offset circumferentially to provide a 90 degree phase shift between the tracks as the wheels rotate on a common shaft. The use of dots reduces blurring of the pulse signals.
A chassis is mounted to the panel and supports the shaft, the printed circuit board, and a rubber dust shield which rubs against the wheels to provide braking action. The chassis, printed circuit board and dust shield all include slots through which the wheels rotate. Protrusions in the printed circuit board slots guide the wheels as they rotate, and protrusions in the dust shield slots rub against the sides of the wheels to provide the braking action.
One aspect of the present invention is an encoder assembly comprising: a wheel mounted so as to rotate about an axis perpendicular to the plane of the wheel, wherein the wheel includes an integral encoder pattern having a track of pattern elements; and a sensor positioned proximate the wheel such that the pattern elements in the track move past the sensor as the wheel rotates. The encoder assembly includes a second track of pattern elements, and further including a second sensor positioned proximate the wheel such that the pattern elements in the second track move past the second sensor as the wheel rotates.
Another aspect of the present invention is an encoder assembly comprising: a plurality of wheels mounted so as to rotate in parallel planes, wherein each wheel includes an integral encoder pattern having a track of pattern elements; and a plurality of sensors, wherein each sensor is positioned proximate a corresponding one of the wheels such that the pattern elements in the track on each of the wheels moves past the corresponding sensor as the wheels rotate.
A further aspect of the present invention is a control console comprising: a panel;
a display having a plurality of display sections mounted on the panel; a plurality of wheels rotatably mounted to the panel proximate the display and arranged so that each wheel is aligned with a corresponding section of the display, wherein each wheel includes an integral encoder pattern having a track of pattern elements; and a plurality of sensors, wherein each sensor is positioned proximate a corresponding one of the wheels such that the pattern elements in the track on each of the wheels moves past the corresponding sensor as the wheel rotates.
An advantage of the present invention is that it provides an inexpensive multiple wheel encoder assembly that is compact enough to utilize commercially available displays.
Another advantage of the present invention is that it eliminates numerous components that are commonly used with encoders.